Mach-DSP User’s Manual
Document Number: MACH-DSP-9021
Page 55
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Position sensor parameters
Galvanometer scanners use LEDs and silicon photodiodes to detect the position of the
rotor. Although the LEDs and photodiodes are made of high quality materials, there are
small differences between each LED and photodiode inside the scanner. To
accommodate these differences, the Mach-DSP provides controls to precisely calibrate
the amount of beam deflection created by the scanner.
Position Sensor scale
(mechanical degrees motion for +10V electrical signal)
This controls the amount of mechanical motion of the scanner to cause +10V to appear
at the input of the Mach-DSP digitizer (and to appear on the test interface connector).
For example, if this is set to 25.0, then a mechanical deflection of 25.0 degrees will
create +10V DC on the digitizer. This also implies that -10V corresponds to -25.0
degrees of deflection. Thus, 20V peak to peak position signal will correspond to will
create 50 mechanical degrees peak to peak (or 100 optical degrees peak to peak)
deflection.
Position Sensor offset
(degrees)
This controls the amount of amount of offset that must be added to the position signal in
order to make a zero-volt command signal to correspond to the center of the projection
surface. This may be used to fine-tune the zero position of the X-Y system, since it is
difficult to precisely achieve centering through mechanical adjustment alone…
Position fault detector
All mirror sets provided by Pangolin are designed to deflect a beam over a prescribed
projection angle. Deflection beyond the prescribed angle will, at the very least, cause
the laser beam to overfill the mirror surface, creating a loss of projected beam power.
Moreover, in some cases if mirrors are deflected well beyond their prescribed range of
angles, they may crash into each other, causing pieces of the mirror to chip away. To
prevent this, the Mach-DSP includes a fault detector, which will shut down the servo
(momentarily) if the position signal exceeds a specified projection angle. Normally this
would only happen accidentally while tuning up a servo, or as a result of some electrical
fault.
Positive-most position before servo fault
(degrees)
This specifies the positive-most position signal that will be allowed before a “servo fault”
is triggered, specified in mechanical degrees.
Negative-most position before servo fault
(degrees)
This specifies the negative-most position signal that will be allowed before a “servo
fault” is triggered, specified in mechanical degrees.
